FISHERY BULLETIN: VOL. 69. NO. 3 



of 3: 1 to 15: 1. In the other, only single L. jollae 

 females were tested and the number of larvae 

 varied to provide ratios of larvae to copepods 

 of 5:1 to 40:1 (Figure 6). The results were 



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LARVAE PER COPEPOD 



Figure 6. — Mortality of Engrmdis mordax larvae, to 

 1 day old, resulting from predation by single Labidocera 

 jollae females. In each experiment 1 copepod was con- 

 fined with 5 to 40 larvae in 3500 ml for 20 hr. The un- 

 broken line is the theoretical 100% larval mortality curve. 



similar in the two experiments; when the ratio 

 was approximately 10:1 or less, it was usual 

 for all larvae to be killed. When more than 10 

 larvae were available per copepod, more larvae 

 were killed per copepod but the mortality 

 dropped below lOOSf. In similar experiments 

 two L. trispinosa females were tested with larvae 

 to copepod ratios varying from 2: 1 to 15: 1. L. 

 trispinosa females were much less efficient than 

 L. jollae females and never killed all the larvae 

 presented to them in 24 hr (Figure 7). Males 

 of both species were similar in killing efficiency 

 to L. t)-ispinosa females. Based on these results, 

 further predation experiments were performed 

 over 20 to 24 hr using 30 larvae with two L. jollae 

 females or five males; experiments performed 

 with either sex of L. trispinosa had 30 larvae 

 and 5 copepods. The comparative predatory 

 ability of labidocerans is shown graphically in 

 Figure 8. The mean number of anchovy larvae 

 killed by L. jollae females was 15. L. trispinosa 

 males and females had mean kills of 4 and 2 



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5 10 15 



LARVAE PER COPEPOD 



Figure 7. — The effect of increasing the density of larval 

 anchovies on the predatory behavior of Labidocera tris- 

 pinosa females. Each dot represents a separate experi- 

 ment with 2 or 3 copepods and from 5 to 45 larvae. 



larvae respectively in 24 hr, markedly less than 

 L. jollae females. The high killing rate by L. 

 jollae females reflects the longer distances and 

 greater volume covered by them owing to tiieir 

 larger size. L. jollae females are approximately 

 0.2 mg dry weight, and males, 0.1 mg. Female 

 L. trispinosa average about 0.1 mg dry weight; 

 males, 0.09 mg. 



EFFECT OF THE AGE OF THE LARVA ON 

 PREDATION BY Labidocera 



We noted in our experiments that Labidocera 

 became less efficient in killing anchovy larvae as 

 the larvae aged. The anchovy larva is 2.5 mm 



660 



